Devices which use disks with a variety of formats such as optical disks, magneto-optical disks, and flexible magnetic-recording disks are known in the art; but, of these, the hard-disk drive (HDD) is widely used, not only in computer systems, but also in electronic equipment such as recording and playback devices for video images and satellite navigation systems.
Magnetic-recording disks used in an HDD are provided with a plurality of data tracks and a plurality of servo tracks formed concentrically. Each servo track comprises a plurality of servo sectors having data addresses. Moreover, each data track comprises a plurality of data sectors which contain user data. The data sectors are recorded between the servo sectors which are divided around the circumference of the magnetic-recording disk.
The HDD has a rotary actuator that rotates back and forth over the magnetic-recording disk; the rotary actuator includes a head-slider. The HDD reads out the address data from the servo sectors using the head-slider, the rotary actuator being controlled on the basis of this address data. By this means the HDD positions the head-slider over a desired data track, and writes data to, or reads data back from, this track.
To increase the magnetic-recording density of a magnetic-recording disk, both the clearance, which is a spacing, between the magnetic-recording disk and the magnetic-recording head that flies in proximity with the recording surface of the magnetic-recording disk, and the changes to this clearance are reduced. Various mechanisms have been proposed to adjust this clearance. One of these provides the head-slider with a heater, adjusting the clearance by heating the magnetic-recording head with this heater. As used herein, this technology is referred to as thermal fly-height control (TFC). With TFC, current is applied to the heater to heat it, causing the magnetic-recording head to project due to thermal expansion. By this means the clearance between the magnetic-recording disk and the magnetic-recording head can be reduced. In addition, methods are known which adjust the clearance between the magnetic-recording head and the magnetic-recording disk using a piezoelectric element, or using a Coulomb force generated between the head-slider and the magnetic-recording disk.
In addition to varying with changes in temperature, clearance can also vary with changes in pressure, which may be produced by changes in the altitude at which the HDD operates. To adjust clearance more accurately, clearance may be adjusted with changes in pressure. As pressure drops, the clearance between the magnetic-recording head and the magnetic-recording disk reduces. For this reason the HDD controls the clearance adjustment mechanism according to pressure changes, which may occur with changes in altitude, and maintains the clearance at an approximately fixed value.
The operation of the HDD is highly dependent on temperature, and in general HDDs are provided with a temperature sensor as a temperature detecting means. The HDD can use the temperature detected by the temperature sensor in adjusting the clearance. In the same way, pressure sensors, or alternatively, altitude sensors, are known as a means of measuring pressure. However, the use of a pressure sensor increases the number of parts required for an HDD. At the same time it also increases the cost of the HDD. However, as described above, clearance varies with changes in the pressure. Thus, within the HDD, changes in pressure can be measured from changes in clearance. HDD's perform clearance adjustment from pressure data calculated from clearance measurement values.
In addition to changes in pressure, extreme changes in humidity and changes in the internal structure of the rotary actuator, or head-slider, which may occur with increased use of the HDD, can lead to changes in the clearance. To more accurately control all the various origins of clearance variation, it is of interest to engineers and scientists engaged in HDD manufacturing and development to determine the variety of factors that may affect clearance, and to adjust clearance accordingly.